Method for pressure treating boards

ABSTRACT

A method for treating wood products is provided wherein wood products are treated in an aqueous solution of a silicate, a rheology modifier, a wetting agent and, optionally, borax and/or a bacteriocide or fungicide; the aqueous solution having a pH of at least 9.0, preferably, a pH of 10-14, and most preferably, 13.0. A suitable dye can be added to the aqueous solution to color the wood product. The present invention is also directed to an aqueous solution for pressure treating wood and a wood product prepared according to the method of the present invention.

This is a division of U.S. patent application Ser. No. 09/303,722, filedApr. 30, 1999, now U.S. Pat. No. 6,235,349, which was aContinuation-in-Part of International Application No. PCT/US97/19812,filed Oct. 30, 1997, designating the United States, which claims thebenefit of earlier filed United States Provisional Patent ApplicationSer. No. 60/029,460, filed Oct. 30, 1996 entitled “Method of PressureTreating Boards.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a formaldehyde-free method fortreating wood products, especially green lumber, to strengthen the woodproducts and to render the wood products flame retardant and resistantto moisture and insects.

2. Description of the Related Art

Prior art publications disclose treatment of wood products withchemicals such as silicates, creosote, copper naphthenate,pentachlorophenol and chromated copper arsenate to preserve the woodproducts and to render them fire-retardant and insect repellant. Aftertreatment, the wood products can be painted, soaked or pressure treatedto coat and/or impregnate the wood products.

U.S. Pat. No. 3,974,318 to Lilla, discloses such a process. In the Lillapatent, a water soluble silicate composition is applied to a woodproduct and the product is subsequently treated with a water solublemetallic salt compound to form a water insoluble metallic silicate inthe wood product.

Although the prior art methods and compositions are suitable fortreating dried lumber and manufactured (engineered) wood products, noproducts or methods have been found suitable for treating green lumberor other wood products having a high water content.

It is, therefore, an object of the present invention to provide a woodproduct treatment method and a compound suitable for treatment of woodproducts, and for treating green lumber as well as to provide a superiormethod and composition for completely treating dried lumber andmanufactured wood products.

SUMMARY OF THE INVENTION

The present invention is directed to a method and a composition fortreating wood produces and a treated wood product prepared according tothe methods of the present invention. The method provides for treatingthe wood products with a silicate based solution that will fullypenetrate and preserve wood products, including green lumber. The methodincludes pressure treating the wood products in an aqueous solution ofsodium silicate which further includes a wetting agent and a rheologymodifier at a pH of at least 9.0 and, preferably, at a pH of at least13.0. Most preferably, the aqueous solution includes a borax and/or abacteriocide or fungicide. Addition of the rheology modifier and thewetting agent to the solution allows the chemicals to fully penetratethe wood product irrespective of whether the wood product is greenlumber or a dried and/or engineered wood product.

The pressure treating method of the present invention includes thefollowing steps: placing the material in a pressure vessel and applyinga vacuum; contacting the material with an aqueous solution andincreasing the pressure in the pressure vessel; draining the aqueoussolution and reducing the pressure, preferably, applying a vacuum; anddrying the treated wood product.

In an alternative method, wood particles are mixed in a slurry of theaqueous solution and a glue; the slurry is injected into a press, forinstance a steam press, and the slurry is pressed to form a board orother engineered wood product. The engineered wood product can befiberboard, particle board or oriented strand board. The wood product isthen cured. As a further alternative, the aqueous solution and/or otheradditives can be injected directly into the press prior to pressing andcuring.

The composition of the present invention is an aqueous solution having apH of at least 9.0, preferably of 10-14 and, most preferably, 13.0 andincludes silicate, a wetting agent and a rheology modifier, the solutionpreferably includes borax and/or a bacteriocide or fungicide.

Lastly, the present invention is also directed to pressure treated woodproduct prepared by one of the above-described methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-c are graphic representations of flame spread distance,temperature and smoke developed versus time in testing of ⅝″ orientedstrand board (OSB) prepared according to the method of the presentinvention.

FIGS. 2a-c are graphic representations of flame spread distance,temperature and smoke developed versus time in testing of ¾″ particleboard prepared according to the method of the present invention.

FIGS. 3a-c are graphic representations of flame spread distance,temperature and smoke developed versus time in testing of ⅝″ Douglas firplywood prepared according to the method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a method and composition fortreatment of wood products which preserves the wood products and rendersthe wood products fire, moisture, fungus and insect resistant. The term“wood products” refers generally to products derived from wood, but isnot exclusively limited to oriented strand board (OSB), medium-densityfiberboard (MDF), plywood, particle board, paper products and naturalwood products, including both green and dried lumber. The treated woodproducts are generically useful for construction purposes. Morespecifically, for purpose of example only, the treated products may beused in flooring, fire doors, exterior beams and columns, fire panelmaterials and sheeting, exterior sheeting including siding, cabinetmanufacturing, furniture manufacturing, railroad cross ties, landscapetimbers, floor plating, fire-retardant lumber, door jambs, sea walls,countertops, exterior fascia material and in window manufacturing.

The method of the present invention utilizes an aqueous solution fortreating the wood products which includes a silicate, a wetting agentand a rheology modifier. The pH of the solution is greater than 9.0,preferably 10-14 and, most preferably, 13.0. In use, for instance, whenthe aqueous solution is used in diluted form, it is desirable tomaintain the pH of the solution at 11.2 to 11.4. The solution mayinclude borax as an insecticidal agent and/or a bacteriocide orfungicide. The relative quantities of components of the aqueous solutionmay be varied, the ranges of the components of the solution arepreferably between 18% and 60% sodium silicate, 0.01% and 2% wettingagent and 0.01% to 2% rheology modifier. Optionally, between 1% and 10%borax and/or 0.1% and 1% bacteriocide or fungicide can be included inthe solution. All percentages relating to the composition of the aqueoussolution are % wt. The remainder of the solution includes water and anyother desirable additive such as a suitable dye or staining agent. Theaqueous solution is most preferably 61.8% water, 38% sodium silicate,0.1% wetting agent and 0.1% rheology modifier. The solution optionallyincludes 5% borax, with appropriate adjustments in the water content. Afurther optional ingredient is 0.2% bacteriocide or fungicide withappropriate adjustments in the water content.

Examples of rheology modifiers include, but are not limited to,thickening agents including cellulosic agents, such as hydroxymethylcellulose, lignum and carboxymethyl cellulose, and acrylic thickeners.Examples of suitable wetting agent include, but are not limited to,metasodium silicate, sodium dodecyl sulfate, sodium lauryl sulfate andtrisodium phosphate. The aqueous solution is preferably prepared having21% solids, or active ingredients, as measured by refractive index. Inuse, the aqueous solution may be diluted to a range between 0 and 21%solids or active ingredients. The suitable dilution for a given woodproduct is determined empirically. For instance, it was empiricallydetermined that MDF and particle board are best treated with a solutionof 8% solids while railroad ties (red and white oak) are best treatedwith a solution of 12% solids.

The bacteriocide or fungicide can be any suitable agent which does notsubstantially affect the ability of the aqueous solution to preserve thetreated wood products. However, it was found that 0.2% CIL-75 (Dow) ormethyl paraben are particularly suitable for this purpose. These agentshave not been previously recognized as useful in wood processing. Inaddition, these agents have the added benefit in that they areenvironmentally safe and are approved for use in food and in foodservice areas.

To treat the wood products according to the present invention, the woodproduct is placed in a pressure vessel. The door of the pressure vesselis closed, and a vacuum of approximately 35 pounds per square inch isapplied. The chamber is flooded with the aqueous solution describedabove.

A pressure of 40 to 160 pounds per square inch is applied to the woodproducts in the aqueous solution. Most preferably, pressure of 40 poundsper square inch is applied for particle board, MDF and OSB and apressure of 140 pounds per square inch is applied for natural woodproducts. During pressure treatment, the aqueous solution is circulatedunder pressure for between 20 and 90 minutes. The wood products arepreferably treated for 30 minutes in the case of particle board, MDF andOSB and 90 minutes in the case of natural wood products. The chamber isdrained and a vacuum of about 30 pounds per square inch is held for 10minutes. The chamber is opened and the treated wood product is removed.The treated wood product is then either placed in a drying kiln andslow-dried for 24 hours with hot air and steam, air dried for 30 days ormicrowave dried for up to 8 hours.

The aqueous solution of the present invention also can be used in avariety of methods commonly used for preparation of “engineered” woodproducts such as, without limitation, particle board, fiberboard andoriented strand board. These wood products are generally prepared byforming a slurry of wood fibers or particles and an appropriate glue.The slurry is placed in a steam press, forming the wood product. Thewood product is subsequently cured. According to one embodiment of thepresent invention, the cured wood product is pressure treated in thepresence of the aqueous solution, as described above.

The wood product can also be treated with the aqueous solution at anearlier stage. In one version of the method of the present invention,the aqueous solution and any additional additives are mixed into theslurry of wood fibers or particles and glue, prior to placing the slurryinto the steam press. Alternatively, the aqueous solution and additivesare added to the press after the slurry is placed into the press.Importantly, the superior penetrating and preservation activity of theaqueous solution according to the present invention allows addition ofthe aqueous solution and/or any further additives at any time during thepreparation of the engineered wood product, or afterward, so long as theaddition of the aqueous solution is physically possible.

EXAMPLES

The fire-retardant ability of this process was evaluated according tothe following procedure by the Hardwood Plywood and Veneer AssociationLaboratory and Testing Service, a commercial testing service, inaccordance with ASTM designation E 84, “Standard Test Method for SurfaceBurning Characteristics of Building Materials.” This 25-foot tunnelmethod is also described by NFPA No. 255 and UL No. 723.

The purpose of the test is to determine the relative performance of thetest material under standardized fire exposure. Results are given forflame spread and smoke developed. The values obtained from burning thetest material represent a comparison with that of ¼″ inorganicreinforced cement board expressed as zero and red oak flooring expressedas 100. The furnace was preheated to a minimum of 150° F. as measured byan 18 AWG thermocouple embedded in cement ⅛″ below the floor surface ofthe chamber, 23¼ feet from the center line of the ignition burners. Thefurnace is then cooled to 105° F. (±5° F.) as measured by a thermocoupleembedded ⅛″ below the floor surface of the test chamber 13 feet from thefire end.

Prior 10-minute tests with ¼″ inorganic reinforced cement board providedthe zero reference for flame spread. Periodic 10-minute tests withunfinished select grade red oak flooring provided for the 100 referencefor flame spread and smoke development.

The wood products tested in the following examples were treated in thefollowing manner. The material was placed in a pressure vessel. The doorwas then closed, and a vacuum of 35 pounds was achieved. The chamber wasflooded with a 32% volume solution of WOF-24, TWF-27 or TWF-27B to apressure of 110 pounds. The solution was circulated for 30 minutes. Thechamber was drained, and vacuum of 30 pounds per square inch was pulledand held for 10 minutes. The chamber was then returned to ambientatmospheric pressure. The chamber was opened and the treated woodproduct was removed and placed in a drying kiln where it was slow-driedfor 24 hours with hot air and steam.

Example 1

WOF-24 Pressure-Treated ⅝″ OSB

A ⅝″ OSB test sample was prepared and tested according to the proceduresdescribed above. The test results are as follows:

Material Tested 1) Manufacturer: World Environmental Irvington, Alabama2) Burn Number 1 3) Average Thickness (in.) .547 4) Average Weight(lbs./sq.ft.) 2.38 5) Average Groove Depth (in.) N/A 6) ProductDescription: WOF-24 pressure-treated ⅝″ oriented strand board Treatementconcentration: 33% WOF-24 7) Color Brown 8) Surface Both sides treated9) Sample Selection Manufacturer 10)  Date of Selection 4/1996 11) Material Description By Manufacturer 12)  Method of MountingSelf-supporting on ledges 13)  Sample Conditioning (days) 22 TestConditions and Data 1) Specimen Preheat Time (min.) 2:00 2) Tunnel BrickTemp. (deg. F.) 105 3) Ignition Time (seconds) 55 4) Time to End ofTunnel 13′ @ 10:00 or Flamefront Distance 5) Time-Distance Curve Area46.9 (min./ft.) 6) Fuel and Temperature a) Fuel (cu.ft./min.) 4.946 b)Max. Vent End Temp. 680 (deg. F.) c) Time to Max. Temp. 9:55 (min.) 7)After Flaming No

Test Results

Test results calculated on the basis of the areas under the curves offlame spread distance, temperature and smoke developed versus time, asshown in FIGS. 1a-c, are provided in the table below for calibrationmaterials and for:

WOF-24 Pressure-Treated ⅝″ Oriented Strand Board Smoke Material FuelDeveloped Description Flame Spread Contributed Index High-density 0 0 0inorganic reinforced cement board Red oak 100 100 100 flooring TestSample 25 20 15

OBSERVATIONS: No burnthrough. Surface charred and flaky to 11½ feet.

REMARKS: The average moisture content of the first panel was 15.2%.

CONCLUSIONS: Based on one test, the flame spread, calculated accordingto ASTM E-84-94, meets Class A (Class I)—25 or under flame spread.

Example 2

WOF-24 Pressure-Treated ¾″ Particle Board

A ¾″ particle board test sample was prepared and tested according to theprocedures described above. The test results are as follows:

Material Tested 1) Manufacturer: World Environmental Irvington, Alabama2) Burn Number 1 3) Average Thickness (in.) .824 4) Average Weight(lbs./sq.ft.) 3.76 5) Average Groove Depth (in.) N/A 6) ProductDescription: WOF-24, TWP-27 and TWP-27B pressure-treated ¾″ particleboard Treatment concentration: 12% WOF-24, TWP-27 and TWP-27B 7) ColorBrown 8) Surface Both sides treated 9) Sample Selection Manufacturer10)  Date of Selection 4/1996 11)  Material Description By Manufacturer12)  Method of Mounting Self-supporting on ledges 13)  SampleConditioning (days) 22 Test Conditions and Data 1) Specimen Preheat Time(min.) 2:00 2) Tunnel Brick Temp. (deg. F.) 105 3) Ignition Time(seconds) 90 4) Time to End of Tunnel 11′ @ 7:30 or Flamefront Distance5) Time-Distance Curve Area 39.2 (min./ft.) 6) Fuel and Temperature a)Fuel (cu.ft./min.) 4.927 b) Max. Vent End Temp. 655 (deg. F.) c) Time toMax. Temp. 9:50 (min.) 7) After Flaming No

Test Results

Test results calculated on the basis of the areas under the curves offlame spread distance, temperature and smoke developed versus time, asshown in FIGS. 2a-c, are provided in the table below for calibrationmaterials and for:

WOF-24 Pressure-Treated ¾″ Particle Board Smoke Material Fuel DevelopedDescription Flame Spread Contributed Index High-density 0 0 0 inorganicreinforced cement board Red oak 100 100 100 flooring Test Sample 20 15 0

OBSERVATIONS: No burnthrough. Surface charred and flaky to 9½ feet.

REMARKS: The average moisture content of the first panel was 16.7%.

CONCLUSIONS: Based on one test, the flame spread, calculated accordingto ASTM E-84-94, meets Class A (Class I)—25 or under flame spread.

Example 3

WOF-24 Pressure-Treated ⅝″ Douglas Fir Plywood

The Douglas fir plywood test sample was prepared and tested according tothe procedures described above. The test results are as follows:

Material Tested 1) Manufacturer: World Environmental Irvington, Alabama2) Burn Number 1 3) Average Thickness (in.) .616 4) Average Weight(lbs./sq.ft.) 2.37 5) Average Groove Depth (in.) N/A 6) ProductDescription: WOF-24 pressure-treated ⅝″ Douglas fir plywood Treatementconcentration: 33% WOF-24 7) Color Brown 8) Surface Both sides treated9) Sample Selection Manufacturer 10)  Date of Selection 4/1996 11) Material Description By Manufacturer 12)  Method of MountingSelf-supporting on ledges 13)  Sample Conditioning (days) 22 TestConditions and Data 1) Specimen Preheat Time (min.) 2:00 2) Tunnel BrickTemp. (deg. F.) 103 3) Ignition Time (seconds) 65 4) Time to End ofTunnel 13½′ @ 9:30 or Flamefront Distance 5) Time-Distance Curve Area54.7 (min./ft.) 6) Fuel and Temperature a) Fuel (cu.ft./min.) 4.933 b)Max. Vent End Temp. 670 (deg. F.) c) Time to Max. Temp. 8:05 (min.) 7)After Flaming No

Test Results

Test results calculated on the basis of the areas under the curves offlame spread distance, temperature and smoke developed versus time, asshown in FIGS. 3a-c, are provided in the table below for calibrationmaterials and for:

WOF-24 Pressure-Treated ⅝″ Douglas Fir Plywood Smoke Material FuelDeveloped Description Flame Spread Contributed Index High-density 0 0 0inorganic reinforced cement board Red oak 100 100 100 flooring TestSample 30 20 15

OBSERVATIONS: No burnthrough. Surface charred and flaky to 12 feet.

REMARKS: The average moisture content of the first panel was 14.1%.

CONCLUSIONS: Based on one test, the flame spread, calculated accordingto ASTM E-84-94, meets Class B (Class II)—75 or under flame spread.

The primary object of the present invention is satisfied by the presentinvention. Prior to the present inventive method, there were nocommercially suitable methods for adequately treating green lumber whichpreserves the lumber and renders the lumber fire, moisture and insectresistant. The present invention is therefore superior for two reasons.First, it provides a method and composition for full penetration ofgreen lumber or other wood products having a high water content as wellas providing a superior method and composition for treating dried ormanufactured wood products. Second, use of a preservative thatpenetrates green lumber is commercially advantageous. Prior art pressuretreatment methods require that the wood products to be dry beforetreatment. Therefore, to adequately pressure treat a wood product, theproduct has to be dried, treated with a preservative and re-dried. Incontrast, wood products prepared according to the present invention neednot be dried prior to treatment, eliminating the drying step and therebyreducing processing costs, labor costs and energy usage.

The above invention has been described with reference to the preferredembodiment. Obvious modifications and alterations will occur to othersupon reading and understanding the preceding detailed description. It isintended that the invention be construed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

What is claimed is:
 1. A pressure treated wood product prepared bypressure treating said wood product with an aqueous solution comprisedof an alkali metal silicate, a wetting agent selected from the groupconsisting of trisodium phosphate and metasodium silicate and a rheologymodifier selected from the group consisting of cellulosic agents andacrylic thickeners.
 2. The pressure treated wood product as claimed inclaim 1, wherein the aqueous solution includes 18-60% sodium silicateand one of 0.1-2% wetting agent, 0.1-2% rheology modifier and 1-10%borax.
 3. The pressure treated wood product as claimed in claim 1,wherein the aqueous solution further includes one of an environmentallysafe bactericide or fungicide and borax.
 4. A pressure treated woodproduct prepared by pressure treating said wood product with an aqueoussolution consisting essentially of an alkali metal silicate; a wettingagent selected from the group consisting of trisodium phosphate andmetasodium silicate; a rheology modifier selected from the groupconsisting of hydroxymethyl cellulose, lignum, carboxymethyl cellulose,and acrylic thickeners; and an insecticidal agent selected from thegroup consisting of borax, a bactericide, and a fungicide.